1. Field of the Invention
The present invention is related to an LED lighting device having multiple driving stages, and more particularly, to an LED lighting device having multiple driving stages for providing wide effective operational voltage range without causing image flicker and uniformity issue.
2. Description of the Prior Art
Compared to traditional incandescent bulbs, light-emitting diodes (LEDs) are advantageous in low power consumption, long lifetime, small size, no warm-up time, fast reaction speed, and the ability to be manufactured as small or array devices. In addition to outdoor displays, traffic signs, and liquid crystal display (LCD) for various electronic devices such as mobile phones, notebook computers or personal digital assistants (PDAs), LEDs are also widely used as indoor/outdoor lighting devices in place of fluorescent of incandescent lamps.
An LED lighting device is normally driven by a rectified alternative-current (AC) voltage and adopts a plurality of LEDs coupled in series in order to provide required luminance. In a conventional method for driving an LED lighting device, the LEDs may be light up in steps in order to increase the effective operational voltage range. The LEDs which are turned on more frequently are aged faster than those which are turned on less frequently, thereby causing uniformity issue. Image flicker may also occur at low rectified AC voltage when not all LEDs are light up. Therefore, there is a need for an LED lighting device capable of improving the effective operational voltage range without causing image flicker and uniformity issue.